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I will probably purchase a Spectra Ventura 150 watermaker for cruising, but am still working with the company to get an acceptable answer to one question. Maybe one of you has dealt with this and can lend some insight.


The Ventura 150 manual states, “The brine discharge thru -hull should be mounted above the waterline, in or just above the boot stripe to minimize water lift.”

My thinking is that this would put the discharge under water whenever sailing on or above a close reach in moderate winds and maybe even on a broad reach given that the boot stripe is only several inches high and cruising boats tend to be fairly heavily loaded. This could put the discharge underwater a good deal of the time. But Spectra says, “IT CAN GO UNDER WHILE HEALED OVER. IT JUST SHOULDN’T STAY UNDER.”

The purpose of keeping it low is to minimize water lift. But if another 6 to 12 inches makes a difference, then it seems like they are operating on the ragged edge of the feed water pump. But the feed water pump is operating at something like 150 psi and 1 foot of water is about 0.5 psi.

Any thoughts on where one should install the discharge?
 

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I'm not sure what their reasonong was. I could see why you want it as close to the waterline as possible. I would think the "brine" that comes out leaves a nice hard water deposit.

I think that if you are heeled over that the waste line will be pointed downhill anyway.
 

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Placing the thru-hull discharge 'higher' than the level of the RO membrane insures that when the unit is shut down the membrane is kept fully wetted when/if the discharge valve is left opened for a short time.
Once the typical polyamide RO membranes are fully wetted out, they should be left fully wetted ... or they can lose their ability to be later 'wetted out' (and they become 'hydrophobic'). Letting a RO / watermaker membrane drain and 'dry out' quickly reduces its efficacy and service life.

My preference is to run an unvented loop to the discharge valve/through-hull, the top of the loop being several feet above the discharge (at the water line). When operating and the loop filled with fluid, there will be no 'static head' differences other than minuscule friction losses as the loop will be operating as a 'siphon'. If when shutting down and I forget to close the discharge through-hull valve, the membrane will stay 'wet' (for a long time) - because of the loop. I prefer also to install a loop at the fresh water/ retentate side, too; and, for the very same reason - keep that membrane WETTED.

With 800 psi potential pressure 'driving' the discharge brine it really makes no difference of a few static height of discharge. Each 2.31 feet of static height of water is equivalent to 1 psi pressure .... pretty minuscule when the high pressure pump is 'driving' at up to 800 psi.
 

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the pointy end is the bow
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With 800 psi potential pressure 'driving' the discharge brine it really makes no difference of a few static height of discharge. Each 2.31 feet of static height of water is equivalent to 1 psi pressure .... pretty minuscule when the high pressure pump is 'driving' at up to 800 psi.
But the discharge line that runs to the thru-hull fitting isn't running at 800 psi, is it? I'm fixin' to install a watermaker in our boat. I've skimmed the instructions a couple times now and I haven't seen the location of the discharge fitting as a concern. The advice I've heard from other folks that have installed one is that it's good to be able to see the discharge and IIRC, it's to confirm that it's running properly.
 

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........ is that it's good to be able to see the discharge and IIRC, it's to confirm that it's running properly.
and you dont have to read a gage to SEE the water coming out !!!! ;-)

If you forget to open the discharge through-hull valve, you can/will get ~800 psi or more 'just before' that discharge exit. Such are the 'features' of 'constant displacement' pumps. :-o
 

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and you don,t have to read a gage to SEE the water coming out !!!! ;-)

If you forget to open the discharge through-hull valve, you can/will get ~800 psi or more 'just before' that discharge exit. Such are the 'features' of 'constant displacement' pumps. :-o
Why would you want a discharge valve? The chances of water pushing back up the line when the discharge thru-hull is below the waterline (while sailing) is not good, there is nowhere for it to go.

The outlet brine is not at 800PSI because it is only the residual water that has squeezed past the pressure control valve. My discharge outlet is 100mm above the water line and the water that comes out is not unlike the average garden hose. I don't have a discharge valve, just a skin fitting. I very rarely run the water maker when sailing, only when motoring or anchored.
 

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Ideally you should have a valve on every through hull fitting below or near the waterline. A surveyor would probably not its omission as well. Hoses can come off.
 

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Good question

I was talking to the Spectra rep at the last boat show. He said a lot of people tie the discharge hose into the sink outgoing hose and port. He did not favor this approach as it is helpful to see discharged outgoing water leave an above the waterline port. I think the sink idea is good and easy but he has a point. Maybe using clear hose one could see the discharge, at the very least, as it heads towards the sink discharge hose?

We will be adding a water maker in the next year or so.
 
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